In a large stockpot, bring 6 cups of salted water to a boil. Add the spaghetti and stir so they don't stick.

In a large stockpot, heat the extra-virgin olive oil and lightly saute the red onion. When the onions are translucent, add the sliced garlic and chile flakes. Saute until fragrant. Add the anchovies, and using a wooden spoon, smash them into the oil. Add the salted capers, parsley, mussels and white wine, and cover quickly, so the steam cooks the mussels. Shake the pot after 1 minute, and again after 2 more minutes. Check the mussels, if they are open and plump, they are cooked.

Drain the pasta in a colander and divide between 4 warmed pasta bowls. Divide the mussels between the 4 bowls of pasta, and pour the wine sauce over, leaving any sandy sediment in the pot.